Earth's atmosphere
Earth's atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth's gravity. It contains roughly 78% nitrogen and 21% oxygen, with trace amounts of other gases. This mixture of gases is commonly known as air. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.
The atmosphere has no abrupt cut-off. It slowly becomes thinner and fades away into space. There is no definite boundary between the atmosphere and outer space. Three-quarters of the atmosphere's mass is within 11 km of the planetary surface.
Temperature and the atmospheric layers
The temperature of the Earth's atmosphere varies with altitude; the mathematical relationship between temperature and altitude varies between the different atmospheric layers:
- Troposphere:. The troposphere is the lowest layer of the atmosphere starting at the surface going up to between 7 km at the poles and 17 km at the equator with some variation due to weather factors. The troposphere has a great deal of vertical mixing due to solar heating at the surface. This heating warms air masses, which then rise to release latent heat as sensible heat that further buoys the air mass. This process continues until all water vapor is removed. In the troposphere, on average, temperature decreases with height due to expansive cooling.
- Stratosphere: from that 7–17 km range to about 50 km, temperature increasing with height.
- Mesosphere: from about 50 km to the range of 80 km to 85 km, temperature decreasing with height.
- Thermosphere: from 80–85 km to 640+ km, temperature increasing with height.
The boundaries between these regions are named the tropopause, stratopause, and mesopause.
The average temperature of the atmosphere at the surface of earth is 14 °C.
The Composition
Percent composition of | |
| ppmv: parts per million by volume | |
| Gas | Volume |
| Nitrogen (N2) | 78.084% |
| Oxygen (O2) | 20.946% |
| Argon (Ar) | 0.9340% |
| Carbon dioxide (CO2) | 365 ppmv |
| Neon (Ne) | 18.18 ppmv |
| Helium (He) | 5.24 ppmv |
| Methane (CH4) | 1.745 ppmv |
| Krypton (Kr) | 1.14 ppmv |
| Hydrogen (H2) | 0.55 ppmv |
| Not included in above dry atmosphere: | |
| Water vapour (highly variable) | typically 1% |
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